In industry nowadays, success or failure depends in part upon knowing the up-to-date status of various assets. For example, in the freight delivery business, up-to-date knowledge of the location and, in some instances, the environment of various assets, such as pallet goods, is critical to efficient and reliable operations. Failure to maintain up-to-date status information can result in temporarily lost assets, sub-optimal use of the assets, and in the case of freight delivery, missed or late deliveries.
Recently, technologies have been developed that greatly assist in tracking locations of assets. For example, global positioning systems (GPS) use wireless signals transmitted by earth-orbiting satellites to calculate the position of a receiving device. Although relatively expensive, GPS receivers are capable of providing relatively accurate location information for virtually any point in the world.
More recently, radio frequency identification (RF or RFID) systems have been developed in which devices, often referred to as “tags,” wirelessly communicate with readers. RF tracking systems are typically used in parcel tracking and sorting, container tracking, luggage tracking, retail tracking, warehouse tracking and inventory operations. The RF tags may be either passive or active. Passive tags absorb signals transmitted by the reader and retransmit their own signals, such as identification information. While passive tags do not require a local power source, their resulting transmit range is relatively short, typically less than 1-2 meters. In contrast, active tags, which send a signal to indicate its location, include a local energy source (such as a battery) that improves transmission range. Depending on the wireless signal system used by the device, the range may be on the order of several meters or several hundred meters. Regardless of the types of tags used, knowledge of the fixed location of the reader devices allows users to identify the location of assets that have tags attached thereto.
Active tag systems are preferred for some applications due to their long range transmission range. Unfortunately, the position signal or “ping” drains battery life of the transmitter, thus resulting in added operational cost of the system.
Obtaining increased system value and decreased operational cost are key business and technical goals for designers of tracking systems. Increasing the value per ping, by decreasing the cost per ping, is one mechanism to decrease the operational cost of active systems. In an exception based asset management environment, the value per ping is the lowest under normal conditions. Merely increasing the period between subsequent pings, however, although it may decrease the cost per ping, does not intelligently decrease the cost per ping, as the extended period may miss critical movement of the tagged asset.